POS Link not working for application

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I have one application in shopify partners which has link

So Whenever some clicks on /apps page it opens with that url.

Now we have developed feature for POS integration. But we are testing it on https://sandbox.getflits.com
Now I added POS cart link in application extension area (https://sandbox.getflits.com/pos/1/popup)  in same application.
But When going to access it in POS android/ios application from cart it opens https://app.getflits.com/pos/1/popup.

This is not normal behaviour. 
Any suggestions would be great.